On Fri, Feb 09, 2024 at 10:32:16AM +0530, Nilay Shroff wrote: > If the nvme subsyetm reset causes the loss of communication to the nvme > adapter then EEH could potnetially recover the adapter. The detection of > comminication loss to the adapter only happens when the nvme driver > attempts to read an MMIO register. > > The nvme subsystem reset command writes 0x4E564D65 to NSSR register and > schedule adapter reset.In the case nvme subsystem reset caused the loss > of communication to the nvme adapter then either IO timeout event or > adapter reset handler could detect it. If IO timeout even could detect > loss of communication then EEH handler is able to recover the > communication to the adapter. This change was implemented in 651438bb0af5 > (nvme-pci: Fix EEH failure on ppc). However if the adapter communication > loss is detected in nvme reset work handler then EEH is unable to > successfully finish the adapter recovery. > > This patch ensures that, > - nvme driver reset handler would observer pci channel was offline after > a failed MMIO read and avoids marking the controller state to DEAD and > thus gives a fair chance to EEH handler to recover the nvme adapter. > > - if nvme controller is already in RESETTNG state and pci channel frozen > error is detected then nvme driver pci-error-handler code sends the > correct error code (PCI_ERS_RESULT_NEED_RESET) back to the EEH handler > so that EEH handler could proceed with the pci slot reset. A subsystem reset takes the link down. I'm pretty sure the proper way to recover from it requires pcie hotplug support.
